Twist rate on .308 Saiga

[Harpoon 0]

I believe that the Saiga has a 1 in 300 or 320mm twist or 1 in 12 or 13 (correct me if I"m wrong). Most US .308s are 1 in 10. That suggests that the Saiga may not adequately stabilize heavier slugs. Does anyone know how heavy you can go at standard velocities? I'd assume 165 is about it, perhaps 180 at shorter ranges. Comments? Thanks, Don.

Edited January 30, 2005 by Harpoon

[Tokageko 8]

According to my understanding of internal ballitics, the Saiga 308 should be able to stabalize anything up to about 168 grains. I plan on loading some cartridges with heavier bullets and will post when I have some more information. I can't say anything definatively, but then again, not many people can on this subject.

 

As I remember them, the rules go something like this: Heavier Bullet = Faster Twist, Faster Bullet = Slower Twist. Logically, the opposites of these apply also. The problem is that both of these effect each-other. Heavier bullets usually go slower and light bullet generally go faster. However, if a heavy bullet is pushed faster, it needs a slower twist rate than normal. The same principle applies to a lower velocity light weight bullet (needing a faster twist than normal).

 

In theory: a given twist rate will be able to stablize any bullet as long as it is going the right speed. In reality, you are limited by the powders available, the length of the barrel, the case capacity, etc.

 

This is all a bit confusing though, so let me share something that might make it a little more simple. The Army's Marksmanship Unit did a lot of testing quite a while ago, on what made a difference in the accuracy of small arms ammunition. What they found was that the quality of the bullet is the most important factor influencing the intrinsic accuracy potential of any cartridge. To re-phrase: Higher quality bullets always shoot better.

 

So, when preparing to reload for accuracy, the bullet used is going to be your most important decision. In particular it should be: the right diameter, as concentric as possible, longer, heavier*, more pointed, and boat-tailed.

 

All that being said, I know that 150's work great in mine, so the next step up is probably in the 160's. It make take some experimenting (within the guidlines mentioned above) to find the right powder/charge, but when you're satisfied with your results for that weight, then you can move on.

 

http://stevespages.com/page8e.htm is a good site with lots of information regarding selection of bullets. I'm sure there are other pages, but that is the only one that jumps to mind right off. As always, stay safe and good luck.

 

*within limits

Edited January 31, 2005 by Tokageko

[RooK 0]

Twist is actually more related to bullet length than weight, although the longer the bullet the more it weighs, but there are exceptions, most notably the Barnes X-bullet. It lacks a lead core and thus the bullet is much longer in order to make up the weight without the core, requiring a faster twist.

 

When the Army's Marksmanship Unit was doing their tests, what variances in accuracy were they looking for, inches or thousandths of an inch? I know one of the guys doing articles in Rifle a few years back was debating about this and did an experiment. He took some bullets and cut them with bolt cutters. The ones that weren't too bad deformed he mashed back into a concentric shape with pliers and proceeded to load and fire them. He was getting 3" @ 100 yard groups despite what would be far from good ammo. Interesting to say the least.

[JWysenski762 0]

what round was it and what kind of rifel was it? 3 inch groups at 100 yards wouldnt be too great for a bolt gun for instance. but still i see your point, that its not bad regardless.

[verdejt 0]

Glad to see I'm not the only one who views Steve's pages. He has a lot of good info there. I even sent him a couple of my manuals in adobe so he could post them up. The rate of twist on a Saiga is actually 1/12.59. In case your interested.

[Tokageko 8]

Thanks Verdejt, I couldn't remember what the actual twist rate was.

 

Rook: As far as the test you mentioned, it is interesting and I'd like to know: Did the article mention any tests past 100 yards? I ask because at 100 yards, the time of flight for bullets fired from high power rifles is generally short enough that even round nosed flat based bullets perform almost the same as hollow point boat tail bullets (slight exageration, but not by much). Also, what kind of groups was the rifle normally capable of, with not deformed bullets?

 

As far as overall accuracy is concerned, there are a lot more factors that go into the equation. In the end, the quality of the rifle could make up for the lack of quality in the bullet at shorter ranges.

 

The other thing I would like to mention is about bullet length. Actually, as far as twist rate is concerned we are both incorrect. Niether weight, nor overall bullet length, is a bad way of gauging the need for a particular twist rate, but the length of the bearing surface of the bullet has more to do with it. Essentially we're looking for how much friction there is between the bullet and the barrel.

 

If I remember correctly the AMU was doing there accuracy testing using National Match M14s and match-grade Winchester M70's from a machine rest, at.... I don't remember what ranges. I could probably find out if you'd like. To answer your question, I'm not "positive" it was thousandths exactly, but they were looking to get as tight a group as possible. Apparently they tried all kinds of variations in powder charge, primers, case thickness, seating depth, and bullet weight. Interestingly enough, they did find that a variation of up to a tenth of a grain of powder made no discernable difference in muzzle velocity. Eventually they stopped trying to make their own match bullets and started buying commercial match bullets instead.

[RooK 0]

I'll have to hunt up the article some time when I feel like sorting through a bunch of mags. Yes, I have a gun rag collection.